Apparatus for combustion analysis



API-i12, 1963 J. A. KUcK rs1-AL 3,084,031

APPARATUS FOR COMBUSTION NALYSS' Filed Jlne 5, 1959 United States Patent O 3?@84 G31 AIARA'EUS FOR IfQh/SEUSTN ANALYSES .lutins Artsen Euch, Cos Cob, and Chesman Henry Bourdeleis, Stamford, Conn., assignors to American Cyanamid Company, New York, NSY., a corporation of Maine Fil-sd lune 5, i959, Ser. No. 81%,356 3 Claims. (Cl. 23a- 253) This invention relates to an apparatus for the cornbustion of materials in an analytical system; and more particularly, to reflective ceramic furnace construction in which the outer shell is of a natural rock which is niachinable in the uniired condition and which when heated becomes hard, strong and resistant. Typical of such materials is cordierite The shell is preferably reflective coating lined. Several furnace sections may be used.

in chemical analysis by combustion, it is common laboratory practice to place the sample to be analyzed in a glass or quartz combustion tube which is then heated to decompose the sample. 'Ille temperatures, sweep gas, and conditions used Vary depending upon whether the combustion analysis is for carbon and hydrogen, nitrogen, sulphur, oxygen, etc. One end of the combustion tube contains catalysts to assist in the breaking down of the sample vapors, after which the products of pyrolysis are passed through absorption reagents.

xernplary of such analysis are systems in which oxygen passes down the combustion tube, burning the sample to water, carbon dioxide, sulphur dioxide, nitrogen, etc. as the combustion products are passed through the combustion tube over a catalyst and through absorption reagents.

. time is usually the most expensive single item in the The timel and temperature cycles and methods vary considerably from analysis to analysis depending upon size of sample, difficulty of combustion, and other variants. ln such analysis, one of the problems is to provide a furnace the sections of which give an accurate, reproducible, rapid heat cycle for the heating of the catalysts, and the heating of the sample, and which may be rapidly cooled to ready the apparatus for a subsequent run.

Furnaces which have been used in the past are shown both in the patent and trade literature. For example, US. Patent No. 2,743,995, P. H. Scherrick, Method of Sample Burning For Micro-Chemical Combustion Analysis, May l., 1956, shows a combustion furnace in which a cylindrical casing of aluminum is used as the furnace shell. As therein described the furnace shell may be hinged and a heating coil wound with an open face so that when the furnace shell is opened, the furnace may be slid axially or laterally to permit the combustion tube to cool rapidly in preparation for a subsequent run.

Laboratory instrument supply catalogues, for instance Catalogue 10i) of E. H. Sargent and Company, at page 327, show a combustion furnace with automatic timing means for controlling the heat cycles of four different furnace sections surrounding a single combustion tube.

ln such combustion analysis it. is desirable `that Vthe furnace be one that can be brought up to temperature as rapidly as desired, a product burned at a selected temperature, and then cooled in a minimum of time so that the furnace is ready for a subsequent sample. One of the biggest advantages of micro-chemical combustion techniques is that one analyst can run a larger number analytical process, any techniques which reduce the cyclic time of analysis represents economic advantages.

lt has now been found that a combustion furnace may be constructed with an outer shell of a natural rock, machinable in the unfired condition. Without being limited thereto, one such roclr is known as cordierite.

Cordierite kis one of the silicates and is referred to in' standard mineralogical texts such as Descriptive Minerology, E. S. Dana, sixth edition, John Wiley, New Yori-t, 1920 printing, at page 419. Also, it appears in The Data of Geochemistry, Government Printing Office, Washinvton, D.C., 19211r at page 409. ln this text cordierite also appears under the synonym iolite. This text gives the speciiic gravity as 2.60 to 2.66; hardness 7 to 7.5; and the color as blue, often smoky or grayish because some of the magnesium may be substituted by iron. The naturally occurring rock has some water in its structure. It is one of the metamorphic rocks and is indicated as being a primary separation from the magmas, its deposition following biotite but preceding the feldspars. Certain pseudomorphs have received distinctive names.

A study of cordierite characteristics is referred to in W. L. Bragg, Atomic Structure in Minerals, Cornell University Press, 1937, at page 183, where is it indicated that the orthorhombic characteristics of cordierite show that it is closely related in structure to beryl.`

Cordierite in its naturally occurring state may be machined with metal working tools. Hence, a furnace shell may be turned on a lathe and formed by milling and tapping and metal working processes to a size and shape which is desired. Whereas a furnace shell may be made of a single piece, it is conveniently made up of several pieces which may be either fastened together with threads, or metal fastening, or may be adhesively united with high temperature cement. The high temperature furnace cements suitable for this purpose are well known to those skilled in the art and conveniently obtainable from suc,L suppliers as the Sauereisen lCernents Company, Pittsburgh, Pennsylvania. For example, Sauereisen electrical resistance cement No. '78 makes a good adhesive cement which may be used to fasten together pieces of a cordierite furnace.`

When a cordierite furnace shell is so formed, it is comparatively soft and tender. The furnace is fired at temperatures at least ras high as the working temperature, for example l1000 C., until the cordierite undergoes a hardening transformation and becomes much stronger and more resistant to deformation. The furnace cements usually must be permitted to air dry for several hours to allow the evaporation of Water and of other solvents after which they are set by the heat treatment. Any forming operations shoud be accomplished before the firing takes place.

Without being limited thereto a-s the only form, the advantages of the present invention may be seen in connection with -a particular embodiment thereof illustrated in the yaccorn-panying drawings, and the following description, in which:

hFGURE i1 shows an exploded view of a single furnace s el FIGURE 2 shows an end view of `a furnace shell in Which the resistance elements .are wound to permit the rem-oval of the furnace shell from the combustion tube.

FEGURE 3 is a sectional view ofthe furnace of Pif"- URE 1 in which the resistance element is coil wound for axial movement only.

As shown in FIGURE l, Aa furnace shell is for-med from a cylindrical shell section of cordierite by turning cylindrical shell section 21 from natural cordierite. For a micro-chemical furnace an exterior diameter `of 21/2 inches and an interior diameter of 2 inches gives a convenient shell. The ends of the cylindrical shell section are stepped. An annular end cap of stepped construction tits into the stepped end of the cylindrical shell section to form a double shoulder joint 23. Each end of the cylindrical shell section is thus closed. The annular end caps have .a combustion tube port 24 of a size to contain the combustion tube to be employed. A port slightly under /s of an inch lits many of the current cornbustion tubes. The cylindrical shell -section and annular endfcaps are cut from a removable section 25. ConvenientlyV the back face of this removable section is a diameter of the shell. The lower face of `the removable section is a transverse horizontal secant sufiiciently far below the diameter of the cylindrical shell section of the furnace that when the section is removed, ythe entire combustion tube is exposed for inspection or cooling. The removable section is provided with tapped Iholes 26 into which `are screwed screw eyelet handles 27. These eyelet handles are conveniently of a heat resistant material such as bronze and are of any convenient shape for the handling ofthe removable sector. Ordinarily eyelets are very handy as metal hooks may be inserted into the eyelets which reduces the chance of `dropping the removable sector when Working therewith.

Under the cylindrical shell .section are 'pedestals 28. These pedestals are conveniently of rectangular sections with slightly rounded corners and are shaped to lit the cylindrical shell section. The pedestals are attached to the cylindrical shell section with pedestal screws 29; The pedestals have tapped holes for the pedestal screws which are preferably countersunk in the inner face of the cylindrica-l shell section. These screws lmay be of stainless steel, heat resistant bronze or other heat resistant material.

rIhe pedestals serve to support the cylindrical shell section and permit the complete furnace to be slid axially or transversely with relationship to a combustion tube 41.

Inside of the shell is a resistance wire -30. As shown in FIGURES 1 and 3, this -Wire may be wound as a free standing wire coil with radial leads 31. Lead ports 32 are cut in the cylindrical shell section, through which the radial leads extend. The radial leads are attached to conductors 33 which feed an electric current into the resistance wire.

The resistance wire .is a wire which will stand a cornparatively high temperature without oxidizing. The ironchromium alloys containing small amounts of cobalt, nickeland copper sold as high temperature resistance wire are suitable for such purposes. An alternate Ycurrent supplied into the conductors from a variable potential transformer is conveniently used as 4an energy input.

Between the pedestals is a therniocouple port 34.

-lIn manufacture, the shell section and the annular end caps and the pedestals are formed from the comparatively soft natural cordierite and assembled togethcrwith a furnace cement such as'Sauereisen electrical resistance cement No. 78, screws inserted, and the assembly is then tired ina inutile furnace at aternperature ofabout 1200o C. until the cordierite has become hardened.

FIGURE 2 shows a different resistance coil shapein which an open sided U-coil is used for fthe `resistance wire. By so forming `the resistance wire it is close to the combustion tube but kyet the-complete furnace may be slid a-Way from the combustion tube to permit more rapid c'ooling of the combustion tube. v

The complete `furnace shell is fairly reflecting, as formed. `lts reflectance may be increased by coating with magnesium oxide. More conveniently fthe reilectance may be increased by placing an inert foil on the interior 4 surface of the furnace. The cylindrical shell section can be lined with a thin platinum foil 36, which is Vplaced in contact with the cylindrical shell section, and which may be bent slightly over the ends of the two sections to aid in holding the foil in position. As shown in FlGURE l a main shell foil section 37 is used to line the main cylindrical shell section. Foil gaps 38 are lleft around the radial leads to Iavoid short circuiting the power supply. A similar removable section foil 39 is used to line the removable section. Preferably, the foil lies against the cordierite and remains in contact with lche cordierite, although a slight spacing is not deleterious.

By having a reflective foil, such as platinum, lining the Shell sections a high internal reflectance is obtained so that heat from the resistance wire is reflected back towards the combustion tube so that the combustion tube is at a higher temperature than the shell itself. The reflection of radiant energy from the lined shell increases the efficiency of the furnace.

With combustion temperatures in the neighborhood of about 1000o C. the cordierite shell with a platinumioil reflective lining lasts indefinitely. The resistance `wire may become glerheated and either distort or burn out. Distortion can be reduced by the insertion of a coil support 40, which may be an additional cordierite, or a ceramic, support which protects the resistance wire coil. This coil support may additionally serve as a thermocouple shell. The coil surrounds the combustion tube 41 which passes axially centrally through the furnace. For even heat distribution it is preferred that the resistance wire coil be fixed so as to be adjacent but not in contact with the combustion tube.

Whereas only one furnace shell is shown, several similar ones are convenientlyV used along a combustion tube where different sections of the tube have different heat programs.

Obviously the size of the furnace shell is adapted to the uses for the particular furnace. Larger shells can be constructed of built up sections. shaped in tongue and groove form, and large furnaces constructed from these smaller segments. The segments may be'designed to so interlock that no cement or other lfastenings are required.

We claim:

'1. An apparatus for `micro-analysis comprising a combustion tube, electrical resistance heat means for said combustion tube, a ceramic furnace for said tube and resistance means comprising a shell of fired cordierite and a reflective foil lining for said ceramic shell in contact therewith.

2. An apparatus for micro-analysis comprisinga com-V bustion tube, an electrical resistance heating means aflixed to said combustion tube and so wound that it may be removed frorn said combustion tube, a ceramicfurnace for said tube and resistance means comprising a shell of fired cordierite having -a readily removable section and a reflective foilrliner for said cylindrical shell section in contact therewith.

3. An apparatus for micro-analysis comprising a combustion tube, an electrical resista-nce heating coil afiixed to said combustion tube and so Wound that it may be removed from said combustion tube; a ceramic 'furnace for said tube and resistance coil comprising a cylindrical shell section of iired cordierite, and perpendicular to `said cylindrical shell section, two planar annular end sections, stepped and cemented into said cylindrical section; a readily removable section comprising a part of said cylindrical shell section and each planar section, said removable section having a back face which is a vertical diam.- eter of the shell, and a lower face that is a transverse horizontal secant sufficiently far below the level of the furnace that when the removable section is displaced, the

entire combustion tube is exposed for inspection and cooling, said removable ,section having tapped Aholes in the cylindrical part of the shell, screw eyelet handles in said The cordierite maygbe tapped holes in the removable section, a separat-e reflective foil liner for each part ofthe cylindrical shell, and a ceramic coil support inside said shell to support and reduce distortion on heating of said coil.

References Cited in the ile of this patent UNITED STATES PATENTS 2,322,159 SaXer June 15, 1943 OTHER REFERENCES Aloe Co. Cata1og 103, Laboratory Apparatus, Equipment and Reagents, 1952, page 294. 

1. AN APPARATUS FOR MICRO-ANALYSIS COMPRISING A COMBUSTION TUBE, BUSTION TUBE, ELECTRICAL RESISTANCE HEAT MEANS FOR SAID COMBUSTION TUBE , A CERAMIC FURNACE FOR SAID TUBE ABD RESISTANCE MEANS, COMPRISING A SHELL OF FIRED CORDIERITE AND 